[sergii]

I'm having a big problem in a chemistry experiment and have no idea how to solve it. I was given a carbonate from Group 1 : X2CO3 were X is unknown. The purpose of the experiment is to find X.

I weighed out 0.99g of the carbonate, dissolved it in distilled water and made the solution up to 100.00cm^3. I took out 10.0cm^3 portions and titrated with 0.100 moldm^-3 HCl.

I carried out a titration and found that the average titre was 32.67 cm^3.

The equation for the reaction would be -

X2C03 + 2HCl = 2XCl + CO2 + H20

Does anyone know how i can find X?

[Borek]

Find number of moles of X₂CO₃ - that plus mass of the sample will give you molar mass of carbonate. That identifies X.

[sergii]

I add the mass of the sample to the number of moles? 0_o

[sergii]

How do i find the number of moles?

[sjb]

How many moles of HCl did you use up in the titration?

[sergii]

It was 0.100 moles of HCl and the average titre was 32.67cm³. So i think the amount of HCl used was 3.267 x 10^-3mol

[Borek]

So i think the amount of HCl used was 3.267 x 10^-3mol

OK, now, from this information and reaction equation - how many moles of carbonate?

[sergii]

Half?

[Borek]

Half of what?

[lann]

If you have the moles of HCl, then you can easily find the moles of the X2CO3.

X₂C0₃ + 2HCl = 2XCl + CO₂ + H20

The ratio of X₂CO₃ to HCl is 1:2.

Let y be the number of moles of X₂CO₃.
1 mole X₂CO₃ / 2 moles HCl = y mol of X₂CO₃ / 3.267 x 10^-3mol of HCl

When you get y, you can find the Molecular Mass (g/mol) of X₂CO₃.
0.99 g / MM of X₂CO₃ = y

Then, when you get MM of X₂CO₃, you can get the MM of X since you know the MM of C and MM of O.  You will do simple math in this case.

I just got the idea due to Borek and sjb's help.  I hope I'm correct.